The present invention relates to an exposure apparatus for forming a pattern image corresponding to at least a part of a desired image on a work to be exposed; and for relatively moving a work table for mounting the work and a mask table on which the pattern is provided in a optical projection system so as to entirely expose the pattern image on the work. More particularly, the present invention is directed to an exposure unit that is capable of detecting the amount of moving of the mask table and accurately executing an exposure operation even if the projection optical system has a magnification error.
In a conventional exposure apparatus, employed in a copy machine, so-called steppers and so forth, are constituted in such a manner that a mask table and a work table are moved relative to each other. It is necessary to control the mask table and the work table so as to be moved with a predetermined relationship with each other in accordance with a magnification of a projecting lens system provided between the mask and the work. In other words, it is necessary to synchronously move the mask table and the work table with each other. To synchronously move the mask table in such an exposure apparatus and the work table, it is necessary to provide some link members for determining the moving amount of one table according to that of the other table, as well as independent feed back systems therefore, and it may be considered that a structure of the exposure apparatus is arranged in such a manner that the moving amount of the mask table is detected on the mask table side; the link members being controlled in accordance with a result of the detection operation; the link members determining the moving amount of the work table by multiplying the moving amount by a predetermined value corresponding to the magnification of the optical system.
However, in the above described structure, because the magnification of the optical system becomes a fixed coefficient, even if there is an error in the magnification, the moving amount is controlled according to the designed magnification including the error. Thus, if there is an error in the magnification of the projecting lens system, the pattern, corresponding to an image on the mask, formed on the work may deflect from the mask pattern based upon the error.